The present invention relates to a motor control device for a hybrid vehicle, and more specifically relates to a motor control device that uses a sensorless vector control to drivingly control one of a motor that is driven by an engine to generate power and a motor that drives a drive wheel. The motor control device of the present invention may be used in a drive device for a hybrid vehicle.
Japanese Patent Application Publication No. JP-A-H11-275884 describes the detection of a position angle of a synchronous motor without the use of a sensor, wherein a biaxial (d-axis, q-axis) current and voltage of a vector control are periodically sampled to calculate an induced voltage, and a position angle θ of a rotor is calculated based on the induced voltage, and the d-, q-axis currents and voltages. This sensorless position angle detection is a high-speed position angle computation that is employed when the synchronous motor is rotating at a speed that enables accurate calculation of the induced voltage. This computation cannot be used when the induced voltage is low and the motor stopped or running at a low speed, because either the position angle cannot be calculated or the calculation has a large margin of error. JP-A-H11-275884 further describes a drive device for a hybrid vehicle that is a combination of an engine, a drive wheel, a first motor, a second motor, and a power train that connects the first motor to the engine and connects the second motor and the engine to the drive wheel.
A drive device for a hybrid vehicle is also described in Japanese Patent Application Publication Nos. JP-A-2002-39008 and JP-A-2005-105957. In order to calculate the position angle, a resolver that generates a position angle signal representing the position angle of the rotor is used; sensorless position angle detection is not performed.
In Japanese Patent Application Publication No. JP-A-2007-236015, an induced voltage of a motor is calculated based on a d-axis voltage command of a motor vector control, and d-axis and q-axis currents of the motor. A position computation then calculates a position angle θ based on the induced voltage, the d-axis voltage command, and the d-, q-axis currents. This is also a high-speed position angle computation.
In addition to the position angle calculation of a motor sensorless drive control based on a vector control, there is a position angle computation that uses a high frequency. This calculation focuses on either running (injecting) a high-frequency current into the motor, or on a harmonic component of a motor current. Orthogonal biaxial inductances Ld, Lq are then estimated based on the high-frequency current, or the harmonic current and voltage, and the position angle calculated using Ld and Lq as parameters. According to this method, even when the induced voltage is low and the motor stopped or running at low speed, there is an injected high-frequency current or a harmonic current that is generated by a PWM control applying a drive voltage. Therefore, the position angle computation can be performed with high computational accuracy. However, when transmitting a high torque (high current), magnetic saturation causes a large margin of error in the estimation of the inductances Ld, Lq. That is, the position angle computation has a large margin of error. Therefore, the position angle calculation focusing on two-axis inductance is a low-speed position angle computation that is employed when the motor is stopped or rotating at low speed.
Hence, an initial state determination was conventionally considered in which, when driving of the motor is started, the three phases are shorted and a predetermined time allowed to pass, after which the three-phase current is detected. If the three-phase current exceeds a threshold, the motor is determined to be clearly rotating and a high-speed position angle computation employed. If the three-phase current is equal to or below the threshold, the motor is determined to be stopped or have uncertain rotation and a low-speed position angle computation employed.